Removing hydrogen sulfide from gaseous process streams can be an expensive, involved, and voluminous venture often involving contact with or use of potentially dangerous chemicals, and producing dangerous and/or toxic materials. Natural gas represents approximately 47% of the products used for fuels, and represents approximately 72% of the products used in the petrochemical industry. Therefore, natural gas is an important resource for the overall energy and petrochemical industries world-wide.
Natural gas is a mixture of hydrocarbons and paraffins, with methane as its principal ingredient, and may include small percentages of ethane, propane, nitrogen, carbon dioxide, sulfuric acid and other materials. Sour gas, or acid gas, is generally defined as natural gas that contains hydrogen sulfide at concentrations up to 20%. Due to the presence of the large quantity of hydrogen sulfide, sour gas is considered toxic. Therefore, before it can be used as natural gas, the sour gas must be treated to remove the hydrogen sulfide resulting in a sweetened natural gas.
The principal objective in treating sour gas is to eliminate hydrogen sulfide (H2S). The most widely used process at this time is the amine process. The most widely used amines are monoethanolamine (MEA) and diethanolamine (DEA) which are most commonly made by reacting ethylene oxide and ammonia. Both amines are irritants to the skin and have a TLV (threshold limit value) of about 3 ppm. Ethylene oxide is an irritant to the eyes and skin, has a TLV of 1 ppm in air and is a suspected human carcinogen; it is also highly flammable, a fire danger and has a high explosive risk. Further, anhydrous ammonia may be fatal in concentrated form, has a TLV of 25 ppm in air, poses a moderate fire risk, and has explosive limits in air of 16 to 25%.
Due to environmental laws, economics and performance, the petrochemical gas and refining industries has seen some dramatic changes in recent years. Present technologies do not address the contaminants found in the final product destined to the consumer and the present regulations with regards to hazardous emissions. Refining and sour gas processing has had very little change in the last 25 years. Refineries, power plants, sour gas treating plants and others are being shut down due to the inability of the processing units to comply with new environmental laws.
As such, there is a need for a method and system to remove hydrogen sulfide from gaseous process streams. Ideally, the method and system would involve less hazardous materials than prevailing methods. Additionally, it is desired that a new method and system be more cost-effective, reduce the size of equipment and area dedicated to processing, improve processing capacity, and produce materials that are non-toxic and non-corrosive.